Probiotics have been shown to modulate gut microbiota function and, when administered in adequate amounts, they may provide health benefits. But with so many probiotic strains on the market, how do we know which ones provide real benefits and what dosage is required to receive them? This is an important question for consumers, and the best way to become informed is to read up on the research. If that seems like a daunting task (and I can assure you that it is) you can relax, because I've consolidated the information in this easy-to-read guide.
First, let's talk about research.
Before we get started, a brief word of caution. Clinical trials involving probiotics have historically been weak because the studies have too few people, are not adequately controlled, and may lack statistical power to draw conclusions. Fortunately, there's a way to mitigate these drawbacks by combining the results from multiple trials. This approach is called a meta-analysis, and it's the only reasonable way to draw conclusions regarding the effect of probiotics on our health.
Is your probiotic working for you?
Below you will find the most common conditions for which probiotics have been evaluated. This list is far from exhaustive but the major categories are included, such as infectious diarrhea, constipation, and irritable bowel syndrome. These sections will introduce the condition and summarize expert opinions on whether or not probiotics have been shown to be an effective treatment.
1. Brain health
Numerous scientific studies have demonstrated that the gut microbiota plays an important role in central nervous system function. Mood and psychological symptoms such as depression and anxiety have been linked to gut microbiota function. Probiotics are known to produce neurotransmitters including serotonin and norepinephrine and may even produce effects similar to antidepressants.
A meta-analysis of trials involving people with preclinical symptoms of depression, anxiety, and perceived stress found that probiotic supplementation resulted in a statistically significant improvement in symptoms compared to individuals taking placebo. Other research studies have made similar conclusions
Allergic diseases such as eczema, asthma, and rhinoconjunctivitis are noninfectious inflammatory conditions that cause us to produce antibodies in response to ordinary exposures to pollen and other allergens. The incidence of these diseases have increased significantly in the last 50 years, and some scientists hypothesize that the increase is due to reduced exposure to microorganisms early in life—resulting in an unbalanced immune response. Since people with eczema and other allergic disease have a different gut microbiota compared to people without allergic disease, it may be possible to alter the microbiota using probiotics in order to alleviate symptoms.
Research on this is mixed; a meta-analysis of 17 clinical trials in which probiotic supplement was provided during pregnancy and early infancy showed that supplementation lowered the incidence of eczema but did not help in treating asthma, wheezing, or rhinoconjunctivitis. However, a separate meta-analysis of 12 randomized controlled trials showed that there was no significant benefit when using probiotics to treat eczema.
And so, current probiotic supplements do not prevent or reduce asthma and rhinoconjunctivitis and probably don't help prevent eczema, but there is still debate regarding the use of probiotic supplementation during pregnancy and infancy for the prevention of eczema. It's important that scientists continue to investigate this area to more fully understand the role of gut microbiota in allergic diseases and to possibly identify probiotic therapies that may be useful.
3. Upper respiratory tract infections
Upper respiratory tract infections can cause fever, cough, and headaches. They are also one of the most common reasons for doctor visits and often result in the inappropriate prescription of antibiotics. Since probiotics have been shown to regulate and support immune function, some trials have been performed to determine whether or not they alleviate symptoms associated with upper respiratory tract infections. A meta-analysis that included 13 randomized controlled trials involving 3,720 people showed that probiotics performed better than placebo in approximately half of the participants. In addition, the duration of acute symptoms resolved approximately 1.89 days sooner when a participant was taking probiotic supplement.
4. Bacterial vaginosis
Bacterial vaginosis (BV) occurs when there is an imbalance of vaginal microbial populations. BV is usually a mild problem and can resolve within a few days; the treatment of BV involves the use of antibiotics, but treatment failures and recurrence are common (i.e., 30 to 40 percent of cases). In addition, the use of antibiotics can result in normal microbiota imbalance and increased incidence of antibiotic drug resistance.
Since probiotics may be effective in replacing depleted Lactobacillus species, studies have been performed to evaluate the efficacy of probiotics in treating BV. A meta-analysis found that there was insufficient evidence for or against the use of probiotics for the treatment of BV. However, we should expect additional studies to define what, if any, role probiotics has in the treatment of BV. For instance, a meta-analysis found that if vaginal lactobacilli are taken following antibiotic therapy they may be effective in preventing recurrent infections. They suggest that an effective treatment regimen may be one that combines standard antibiotic treatment with long-term probiotic supplementation.
5. Urinary tract infections
Urinary tract infections (UTI) occur when bacteria invade the urinary system and begin to multiply in the bladder, kidneys, ureters, and urethra. UTIs are more common in women, and doctors usually treat them with a course of antibiotics. A limited number of trials have been performed to assess the efficacy of probiotic supplementation in the prevention of UTIs. A meta-analysis of nine studies and 735 people found no significant benefit associated with the use of probiotics in the prevention of UTIs. However, the authors caution that a benefit cannot be ruled out due to the small number of well-controlled studies.
6. Inflammatory bowel disease
Inflammatory bowel disease (IBD) is a gastrointestinal tract disorder characterized by recurrent episodes of inflammation of the digestive tract resulting in severe abdominal pain, bloody diarrhea, weight loss, and fever. IBD includes Crohn's disease (CD) and ulcerative colitis (UC). The cause is unknown, but genetics and immune system dysregulation are known to play a role. Since probiotics are thought to alter the gut microbiota composition and function and play a role in reduced inflammation, many researchers have evaluated probiotics as a treatment option for IBD.
In an extensive review of 36 meta-analyses and systematic reviews of probiotic treatments for IBD, researchers concluded that additional studies are required and the jury is still out on whether or not probiotics are an effective therapeutic option for IBD. Patients with IBD should always consult with a qualified provider regarding the use of probiotics.
7. Irritable bowel syndrome
Irritable bowel syndrome (IBS) is a chronic condition that is characterized by intermittent abdominal pain, diarrhea, constipation, bloating, and gas. There is currently no cure, and conventional therapy is aimed at reducing symptoms, with little success. Modulation of the gut microbiota by the use of probiotics may provide an attractive therapy to assist in the treatment of IBS.
The use of probiotics for the treatment of IBS has been extensively studied. One meta-analysis involving 43 randomized controlled trials showed that probiotics had beneficial but modest effects on IBS symptoms including abdominal pain, bloating and flatulence. Additional work is needed to better understand the optimal dosage, strain type, and subgroups of patients who are likely to benefit.
Treatment of constipation may include laxatives, stool softeners, and bulking agents that increase food volume and weight. However, up to 47 percent of the 3.2 million patients that visit medical centers annually are not completely satisfied with such treatments. Since probiotics may improve gut function in people with constipation, a meta-analysis of 14 randomized controlled trials involving 1,182 patients with constipation was performed to assess the efficacy. The analysis concluded that probiotics improves gut transit time by 12.4 hours, increased stool frequency by 1.3 bowel movements per week, and improves stool consistency.
9. Heart health
Hypercholesterolemia is the medical term used to describe high levels of blood lipids and has been identified as a risk factor for atherosclerosis and cardiovascular disease. Many people with mild hypercholesterolemia are interested in using natural remedies (instead of prescription drugs) for lowering lipid levels. One study evaluated 11 randomized clinical trials involving people that were not taking cholesterol-lowering agents and found that probiotic intervention lowered total cholesterol and LDL cholesterol compared to people who did not take probiotic supplements. Levels of HDL cholesterol were unaffected.
10. Blood pressure control
Blood pressure readings are a measurement of the systolic (i.e., pressure in the arteries when the heart pushes blood to the rest of the body) and diastolic (i.e., pressure in the arteries when the heart is at rest) pressure. High blood pressure has been strongly associated with a risk for chronic disease such as cardiovascular and kidney disease. A meta-analysis involving nine clinical trials demonstrated that probiotic supplementation reduced systolic blood pressure by 3.56 mm/Hg and diastolic blood pressure by 2.38 mm/Hg.
11. Infectious diarrhea
Let's face it: No one looks forward to a bout of infectious diarrhea, yet we've all faced it. In the United States, episodes of infectious diarrhea occur in children an average of two times per year, and foodborne diarrheal illness results in approximately 48 million cases per year, resulting in 128,000 hospitalizations. Infectious diarrhea typically resolves in three to seven days, and there is strong consensus that probiotics are efficacious in limiting the duration of infectious diarrhea. In a meta-analysis of 63 trials and 8,014 people, many of whom were infants and children, researchers showed that probiotic therapy shortened duration of diarrhea by 25 hours and reduced stool frequency.
12. Glycemic control
Hyperglycemia is the medical term used to describe high levels of blood glucose and is associated with several chronic diseases such as diabetes, cardiovascular disease, and obesity. Lifestyle changes including diet and exercise are most often used to bring glucose levels back under control. Since alterations in gut microbiota are seen in patients with diabetes and obesity—and since probiotics are known to have an effect on the gut microbiota composition and/or function—some have suggested that probiotic supplementation may provide a natural remedy for hyperglycemia. A recent meta-analysis of 17 randomized controlled trials involving 2,528 participants concluded that probiotic supplementation lasting for at least eight weeks has a statistically significant but modest effect in lowering fasting blood glucose levels.
13. Weight loss
The gut microbiota of people with obesity display significantly less microbial diversity compared to people without obesity. These findings suggest that increased microbial diversity may promote weight loss, and since probiotic supplementation may improve gut microbiota diversity, some have suggested that it can be used to assist in weight-loss efforts.
Recent literature reviews and meta-analysis were performed to evaluate the current status of probiotics as a weight loss therapeutic. The authors found that probiotics are not effective for weight loss. Clearly, research in this area is insufficient, but so far, not enough evidence in the literature exists to recommend probiotic supplements for weight loss efforts. It is possible that additional probiotic strains may prove effective. Also, a more personalized approach to probiotic supplementation for weight loss may produce better outcomes.
What else is there to know about probiotics?
The internet is awash with recommendations about which probiotic strains work best, and it seems that everyone has an opinion. But when opinions are not backed up by scientific evidence—we should all be suspicious. Here are some additional tidbits to remember:
- Everyone is unique: In previous posts I've described how each of us has different genes and gut microbiota composition, which affects how probiotics interact with our bodies. Because of these differences, a specific probiotic strain may work for one person but not for another. Remember this when choosing your probiotic. If a strain or formulation isn't working, in most cases it's OK to switch things up and try something new. If you've been prescribed a probiotic formulation for a specific condition, remember to check in with your doctor before making changes.
- Not all probiotics work the same way: Most probiotics are strains of bacteria that were isolated from the intestinal flora of healthy volunteers. Consequently, they are fully equipped to interact with our bodies to deliver a health benefit. In a previous post I explained how probiotics function in four ways to promote health, and it is useful to understand these mechanisms as you make choices regarding the best probiotic for you.
- Your diet matters: Be aware that you already have a full complement of beneficial microbes in your body that are ready and able to work in your favor. Adding probiotics contained in foods and supplements can help but if you are consuming a diet that is devoid of prebiotic foods such as vegetables you are not going to reap long-term health benefits. The beneficial microbes in your gut, along with the probiotic strains that you may add to your diet, need healthy foods to survive and thrive.
- Not all strains are the same: The health benefits ascribed to probiotics are only valid on the strain level. In other words, if you intend to use this guide to make decisions on which probiotics might work for your situation, remember to check out the strain designation. For instance, all Lactobacillus acidophilus strains are not the same. The health benefits ascribed to Lactobacillus acidophilus LCFM may not also apply to Lactobacillus acidophilus DDS-1.
- Consult a professional: Finally, if you are being treated for a specific condition, remember to check in with your health care provider for guidance on which probiotic will work for you.